Acoustic absorbing materials integrally made from a nonwoven fabric layered at least on one side of glass fiber mats, urethane chips, and the like processed by binder resins such as phenol resins are now available (see, for example, Patent Document 1). To improve the covering properties of the acoustic absorbing materials, the fluffing resistance and design properties of the surface need to be imparted by increasing the fiber content of nonwoven fabrics in the surface layer or increasing the fiber compression bonding rate in thermocompression bonding.
However, although the covering properties may be improved by increasing fiber compression bonding rate, the forming processability decreases since the constituent mutual fibers are elongated or displaced largely in hot press forming process. Furthermore, that arises another problem of high cost due to productive inefficiency since the time for the forming process would be prolonged.
Acoustic absorbing materials including needle-punched nonwoven fabrics (see, for example, Patent Document 2) have weak interfiber bundling and thus good formability. However, there is a problem that decrease the operability since it is difficult that such acoustic absorbing materials are hold by a pin tenter, which is used for binder processing to impart fire retardancy, and water and oil repellency. Furthermore, that arises another problem of high cost due to many manufacturing processes.
Thermocompression-bonding filament nonwoven fabrics are characterized by low cost due to reduced manufacturing processes, and strong interfiber bundling through fiber compression bonding. Thus, it leads to poor molding properties. The molding properties can be improved to some extent by processing at weak compression bonding after changing the heating temperature and pressure condition during embossing. However, such nonwoven fabrics still suffer from the tendency of fluffing due to breaks or partial breaks of embossed marks provided as design properties. In addition to this, there is a technique to allow constituent fibers to be easily stretched by reducing the spinning speed in the manufacture of nonwoven fabrics to reduce the molecular orientation of constituent fibers. This technique, however, has a problem to tend to lose the evenness of webs to form spots or to increases the shrinkage of constituent fibers to generate shrinkage spots during molding.